XS Breather Valve mod

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I know them as rat tails, hose tails and serrated tails in the Americas I've heard them called barbed tails. Hell! call 'em what you want :wink: I do.

Cash
 
An observation on Reed valve as a power benefit to a race engine, it won't. The negative pressure may help keep oil in, but it causes suction against the rising pistons. Race motors breathe out into a catch botle, the oil vapour condenses and is trapped within. The outlet from the bottle goes to atmosphere. Both inlet and outlet hoses are the same diameter and the catch bottle should be equal to or greater than the engine capacity.

the standard post 71 Commando set up of the engine breathing into the oil tank and then out into the air filter chamber was an EPA issue. This also condenses the expelled vapour and its dirty blow by into the oil tank which is an undesirebable contamination. I use a catch bottle and vent to atmosphere for the crankcase breather and have an additional 4mm hose from the top of the inlet rocker cover vented to the end of the rear mudguard. No oil leaks on this bike.

Mick
 
hi mick my breather set up is almost the same as yours only difference is the pipe from my inlet rocker cover goes into catch tank mikesxs site states that fitting a reed valve breather to earlier xs 650 models shows a slight power increase on the dyno so i assume the earlier ones did,nt have the read valve breather.dunstall used a g50 type flap valve in the end of the crank which works on same principle as a reed ie pistons going down blows the valve open, pistons comeing up sucks it closed,
 
Somewhere I read Nascar engine builders were spending a lot of money to create negative (vacuum) crankcase pressure. Anyway, having a one way device in the breather line of a Commando will definitely reduce oil leaks, especially those of the crankshaft to primary case variety.
 
An observation on Reed valve as a power benefit to a race engine, it won't. The negative pressure may help keep oil in, but it causes suction against the rising pistons.
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I've got to admit sitting on the fence regarding oil leaks and small power claims. However, surely at optimum revs more energy is wasted pumping air in and out of the crankcases than suction against rising pistons as that very suction will pull them back down. Anyway, it would be interesting to see a dyno test.

Personally, I started fitting breather check valves in the 60s to stop grit and dirt etc getting sucked in to the oil tank 8) well I thought it was a good idea then.

Cash
 
hi cash i was thinking along those lines too and if what jim says is true then the nascar boys are onto it too.i would be interested to see a dyno report on the with and without valve. also i have noticed that pre 71 commando riders dont query breather problems,ie the ones fitted with disc valves off the end of the cam.dr hiller where are you on this
 
Cash, The dyno work has been done by Jim Comstock engineering in Colorado. Jim discovered that breathers beyond the 3/8 pipe size used on a Norton stock are parasitic but that a high quality one way valve that is up to the job must also be used. Since the oil cap on the tank breathes there is no way to pressurize the tank with the little air coming out of the cases. Since at operating 3000 RPM it is almost Nil.
 
Hi Norbsa,
a high quality one way valve that is up to the job must also be used
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Couldn't agree more I've seen a few horrors. A well known supplier was selling a standard brass domestic check valve fitted with the standard spring, it took near 10psi to open .

Since the oil cap on the tank breathes
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I didn't think the commando oil cap breathed, it hasn't a hole and there's a vent pipe in the neck?

Cash
 
Thankyou "everybody" for your knowledge and advice on this topic!


Great mates.

Brewer.
 
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